The present invention relates generally to laminated fire-resistant doors and relates more particularly to a fire-resistant door utilizing a central core of mineral faced with a fiber mat, preferably of glass fibers.
Fire doors, as used in residential, commercial and industrial applications, are typically employed in conjunction with fire walls to provide fire protection between different zones of a structure, and particularly to isolate high fire risk areas of a building from the remainder of the structure, such as the garage of a dwelling from its living quarters. Fire doors are usually not capable of indefinitely withstanding the high temperature conditions of a fire but rather are designed to maintain the integrity of the fire wall for a limited time to permit the occupants of a building to escape and to delay the spread of the fire until fire equipment can be brought to the scene.
Various tests have been devised for fire doors and are based on factors such as the time that a given door would withstand a certain temperature while maintaining its integrity, and hose stream tests which involve the door's ability to withstand the forces of a high pressure water stream. The American Society for Testing Materials (ASTM) has devised tests to establish fire door standards and these standards are incorporated into building codes and architectural specifications. One such standard, ASTM Method E 152, requires a door to maintain its integrity for twenty minutes while withstanding progressively increasing temperatures reaching a maximum of 1462.degree. F. The fire door of the present invention meets the requirement of this test.
Considerations in fire door design in addition to retarding the advance of a fire, include the cost of raw materials and the cost of fabrication. Furthermore, the weight of the door is important both from the standpoint of ease in handling and the cost of transportation. The strength of the door is also an significant factor since fire doors must pass water stream tests as well as have the requisite structural strength to withstand normal use and abuse.
Fire-resistant doors have been made in a variety of constructions utilizing a number of materials including wood, metal and mineral materials. Early forms of fire doors comprised simply wooden cores faced with metal sheeting. Although wood of ample thickness is an effective fire and heat retardant, the doors of such construction tended to be heavy, and were expensive to fabricate and transport.
Mineral materials have also been employed in the manufacture of fire doors. The core of a commercially-available metal fire door principally comprises a composition including mineral fibers and a binder. Such doors suffer, however, from a lack of strength and the handling of the cores, which are friable, results in the production of irritating dust particles during the manufacture process.
It has also been proposed to make fire doors wherein the core comprises particles of expanded perlite which are bound together by the use of various hydraulic binders including gypsum, cement and inorganic adhesive material. In order to provide sufficient strength, particularly to withstand handling of the core during manufacture, the core is compressed to compact the mixture to a relatively high density, resulting in a relatively heavy door weight.
Other fire door proposals have included the use of conventional gypsum wallboard panels as a core material. However, in order to provide sufficient fire resistance, the thickness required of the wallboard is such as to result in an excessively heavy door. Furthermore, internal structural members such as rails or mullions have been found necessary to support and strengthen wallboard panels. The need for such reinforcing elements increases the cost of materials and assembly of such doors, and, by dividing the core into sections, results in internal seams in the door core structure through which flame and smoke can penetrate under fire conditions.